A non-commissioned officer (sometimes noncommissioned officer), or NCO, is an enlisted member of an armed force who has been delegated leadership or command authority by a commissioned officer.

The non-commissioned officer corps is the junior management of the military. An experienced NCO corps is a very important part of Western armies; in many cases NCOs are credited as being the metaphorical "backbone" of their service, and of their individual units.

Typically NCOs serve as administrative personnel, as advisors to the officer corps, and as both supervisors of, and advocates for, the lower-ranking enlisted personnel.

The NCO corps includes all the grades of sergeants and corporals. The Naval equivalent includes all levels of petty officers.

Some have compared the centurions of the Roman Army with modern NCOs. At some levels this may be an apt comparison; however, the senior centurion of a legion was responsible for training and leading a unit of as many as 4,000 men and had the powers and responsibilities of a modern colonel.

United Kingdom

In the British Armed Forces, NCOs are divided into two categories. Lance corporals, corporals and lance sergeants are Junior NCOs (JNCOs). Sergeants, staff sergeants, colour sergeants, and (in the Royal Air Force) chief technicians and flight sergeants, are Senior NCOs (SNCOs).

Warrant officers are often included in the SNCO category, but actually form a separate class of their own. SNCOs and WOs have their own messes, which are similar to officers' messes (and are usually known as Sergeants' Messes), whereas JNCOs live and eat with the unranked personnel.

The Royal Navy does not refer to its petty officers and warrant officers as NCOs, but calls them Senior Ratings (or Senior Rates). Leading ratings and below are Junior Ratings.

See also

• Military ranks
• Comparative military ranks